Primary lithium cells comprise a lithium anode, a cathode, a separator between the anode and the cathode, and an electrolyte within a hermetically sealed casing. The term lithium includes cells using lithium, a lithium alloy or other lithium-containing materials. Examples of typical primary lithium based cells can be obtained from Greatbatch, Inc. in Clarence, N.Y., including their Electrochem Commercial Power division.
For this application, a plurality of cells is referred to as a battery. These cells and batteries are used in applications where high energy density are required and where frequent cell replacement is undesirable.
A primary lithium cell becomes unstable when the cell is run down beyond its useful life. It is understood to those of ordinary skill in the art that the useful life of a primary lithium cell, for example of a moderate rate size D unit, is complete when it is depleted below 1.5 volts as measured over an open circuit.
When the cell becomes unstable, the primary lithium cell can swell beyond the casing's burst pressure. If such swelling occurs, the electrolyte can leak from the casing. The leak can be slow, rapid or anywhere in-between. What ever the leak rate, electrolyte leaks are undesirable and can damage that which is being powered by the cell.
It is desirable to decrease the chance of a primary lithium cell becoming unstable when it is connected to a load. The present invention addresses at least that problem.